In this day and age when there is concern regarding the dependence on oil by a future motorized society, people are expecting that automobiles equipped with a hybrid fuel cell system will become popular. The hybrid fuel cell system includes a fuel cell and a battery (secondary cell) as power sources. The fuel cell and the battery are connected in parallel with respect to a load, and high-voltage converters for converting voltages are arranged between the fuel cell and the load and between the battery and the load, respectively.
A load applied on a hybrid fuel cell system installed in vehicles such as automobiles greatly varies as compared to a load applied on a stationary hybrid fuel cell system which is installed in buildings.
Thus, the revolution speed of each pump which supplies reactant gases (an oxidant gas and a fuel gas) to a fuel cell greatly varies in response to the variation of load. For example, when a driver suddenly stops pressing down an accelerator (see al in FIG. 3), the load is greatly reduced. The revolution speed of each pump needs to be reduced in accordance with the reduction of the load. In the related art, as disclosed in patent document 1, the revolution speed of each pump has been reduced in response to the reduction of the load by a regenerative control for each pump (i.e., by operating a motor of each pump as an electric generator, converting a mechanical energy to an electric energy, and returning the electric energy to a power source, etc.) (see α2 in FIG. 3).